This invention relates to the elimination of undesired plants or parts thereof.
In the agriculture of various crops, required weeding or defoliation is commonly achieved by the application of chemicals or by flaming. The number of chemicals which can be legally used is restricted by health and environmental considerations. An approved chemical must present no health hazard to agricultural workers and must be free of environmental hazards, e.g., toxicity to birds and animals as well as contamination of water supplies. Furthermore, chemicals are slow acting so that their efficacy develops over a period of several days. Hence, rain can easily wash away a chemical before it has brought about the desired defoliation or weed destruction. The use of flames or, more broadly, heat to kill unwanted plants or foliage requires great care which translates into a high labor cost. Moreover, with many crops flaming or exposure to high temperatures is impractical because it cannot be confined to only undesired plant material.
Several forms of tunnel-like ovens adapted to straddle a row of plants and to move along the row to effect thermal plant conditioning have been disclosed as illustrated by U.S. Pat. Nos. 2,682,728, 3,477,174 and 3,626,636. The number of designs which have been proposed for such tunnel-like ovens suggests that thermal treatment of plants involves many difficulties.
One of the chemicals used to defoliate cotton plants prior to the harvesting of the cotton is superheated ammonia vapor as described in U.S. Pat. No. 3,238,667. Besides the cost of ammonia and the fuel required to convert liquid ammonia into superheated vapor, ammonia used as a defoliant has the further disadvantage of being a fertilizer which under certain ensuing weather conditions can promote second growth of new leaves.
In summary, while several chemicals and different forms of flaming are used to destroy weeds and to defoliate plants, each has inherent disadvantages.
Accordingly, a principal object of this invention is to achieve desired weed control and defoliation without creating any health or environmental hazards.
A further object is to use inert liquefied gases to eliminate undesired plant material.
These and other objects and advantages of the invention will be evident from the description which follows.